Wireless mobile communication technologies and devices have been applied widely in daily life and work, releasing space-time constraints in communications and offering great convenience for people. However, since there is no space-time confinement, communication environment may be complex and variable, which includes a noisy environment in which noises may severely degrade quality of speech communication, therefore speech enhancement technologies for suppressing noises play a significant role in modern communication.
In common speech enhancement technologies, there is a single microphone spectral subtraction speech enhancement technology also called single channel spectral subtraction speech enhancement technology, such as those disclosed in the patent document 1 (CN1684143A) and patent document 2 (CN101477800A). This technology has the following defects: Firstly, only steady-state noise can be suppressed, and there is no significant suppression for non-steady noise such as surrounding talking in supermarkets. Secondly, in a case of low SNR (signal to noise ratio), noise energy can not be evaluated accurately, hence damaging speech. Finally, this technology spends long time evaluating noise energy, therefore noise reduction works only after a period of noise occurrence.
The patent document 3 provides a better speech enhancement technology using a microphone array consisting of two or more microphones in which noises received by one microphone are used by an adaptive filter to counteract noise component in signals received by the other microphone and maintain speech component. Since in practice, signals received by both microphones contain speech components, speech may be damaged while reducing noises, therefore a critical difficulty of this technology is how to control convergence and filtering of the adaptive filter to protect speech in one microphone from being counteracted by speech in another while effectively suppressing noise.
In patent document 4, the microphone array has a directivity by designing specific locations of microphones, while in patent document 3, a directive microphone is used, which has different energy responses to signals from different directions, and determines signal directions by comparing energy differences to control noise elimination. However, this method imposes strict requirements for microphones, such as consistency of microphones or a directive microphone needs to be designed carefully to have significant directivity, hence having great limitations; secondly, using this method, in a case of an environment with high noises, speech state can not be accurately determined, thus the noise reduction process of adaptive filter can not controlled accurately, hence speech may be damaged while reducing noise.
Patent document 1: China patent of invention publication CN1684143
Patent document 2: China patent of invention publication CN101477800
Patent document 3: China patent of invention publication CN101466055
Patent document 4: China patent of invention publication CN101466056